Accepted Answer

I believe that work on SPICE support began around the 4.1/4.2 timeframe. It also required some changes to QEMU apparently. As such, any SPICE code in 4.1 (if there is any) is probably quite weak and reliant in part with having a good QEMU available.

The Xen Project 4.4 release had a lot of improvements to the SPICE support. If you want to use SPICE, you will do much better with the latest release. If you stay with 4.1, you may not get it to work well (or work at all).